Electronic keys for motor vehicles are known; they differ from traditional mechanically cut keys with mechanical notching by being able not only to mechanically release the steering column when inserted into the corresponding lock located in proximity to this column, but also to enable the electronic control unit (immobilizer), which in its turn controls particular units vital for the motor vehicle operation. This further function is performed by radio or infrared reception/transmission signals.
These electronic keys have certainly increased the safety level of motor vehicles against theft, even though the digital information contained in their memory can be easily read and be memorized in a cloned key, which can be freely used instead of the original key.
In order to avoid these drawbacks and to make electronic key duplication more difficult, it has been proposed (U.S. Pat. No. 5,596,317) to use, for information exchange between the electronic key and the motor vehicle vital units, a personalized algorithm with a non-readable secret code, which differs from vehicle to vehicle. When the key is inserted into the corresponding vehicle ignition switch, its control unit generates a random number and transmits it via radio to the key, which processes it with a personalized algorithm, and returns the result of this processing to the control unit. The control unit, which already possesses the personalized algorithm, executes reverse processing to obtain the random number, and then compares it with the number originally generated. The same procedure then takes place between the control unit and the other vital units of the vehicle.
In this case, key duplication is evidently made more difficult given the ignorance of the secret key code.
WO 2008/14199 has also solved the problem of duplicating keys provided with a non-readable secret code. In particular, to identify that code, all the readable data of the original key are transmitted by the authorized duplication centre to a remote computer managed by a person in possession of the non-personalized algorithm and able to obtain the secret code from the result of processing this by the key using the personalized algorithm, and which is then transmitted to the duplication centre for use in duplicating the original key.
A drawback of this solution is that the electronic key can be read and be duplicated by equipment possessing the non-personalized algorithm.
In order to also eliminate this drawback and make the duplication of an electronic key even more difficult, so-called mutual recognition or mutual authorization keys have been proposed.
These are provided with a head housing a receiver/transmitter (transponder) able to dialogue with the electronic control unit of the immobilizer on board the vehicle, to recognize the code and be recognized thereby (mutual authentication).
For this purpose, the memory associated with the key transponder stores a unique identity number (ID), at least one non-readable code (SK), a response code (RESPONSE) and possibly a set of other data, which overall form the memory “pages”.
The mutual authentication provides for the key, once inserted into the vehicle ignition switch, to transmit its ID via the transponder to the control unit. This, on verifying that the key ID corresponds to one of the IDs inserted into its memory, sends to the transponder a first random number (RND) followed by a second number (SIG) obtained by a specific algorithm (f) based on the key identification code ID, on the first random number RND, and on the non-readable SK code memorized in the control unit and identical to the non-readable key code (SIG=f(ID, RND. SK).
The key, in possession of the first random number, then makes the same calculation using the same algorithm f, the ID and SK data which it possesses and the RND value received from the immobilizer control unit. If the result of this calculation is identical to the second number SIG received from the control unit, this signifies that mutual recognition has occurred between the key and the control unit; the key transmits the RESPONSE to the control unit, i.e. the signal that mutual recognition has taken place, together with any other data memorized therein, the control unit then enabling the ignition operations.
In practice it is frequently necessary to duplicate an electronic vehicle key of the aforedescribed type, starting from the original or from an already enabled key, however this duplication, i.e. the electronic coding, is extremely complex, given the impossibility of obtaining the non-readable SK code of the original key together with all the other data, excluding the identification number ID, stored therein and required for obtaining mutual control unit recognition.
In order to solve this problem it has already been proposed to read, with a traditional transponder reader/writer, the ID code of the original key to be duplicated and, after having written it onto a new key previously mechanically notched to correspond to the original key, to then make at least two successive vehicle instrument panel activation attempts. These two attempts will evidently not be successful, but they enable two first numbers RND1 and RND2 and two second numbers SIG1 and SIG2 to be recovered from the control unit which have been generated following recognition of the identification number ID.
These numbers, when transferred into the transponder reader, enable this to determine the non-readable SK code of the control unit by calculating it with the inverse function f−1, already implemented in the transponder reader software.
With this and with one of the pairs of RDN and SIG data previously acquired by the new key and transferred thereby to the transponder reader/writer, it is possible to read from the original key, via the reader/writer, all the other data stored therein and to write them into the new key, which becomes to all effects a clone of the original key.
This known method overcomes all the past obstacles in duplicating this type of electronic key which were due to the impossibility of acquiring the non-readable SK code from the original key, essential to duplicate the electronic part of the key, however at the same time it has presented certain drawbacks, which the present invention proposes to eliminate.
A first drawback consists of the fact that the method operates on the assumption that by means of its attempts to recognize the new key inserted into the vehicle ignition switch, the immobilizer control unit thereof transmits at least two separate RDN numbers and at least two separate SIG numbers necessary to determine the non-readable SK code via the inverse function f−1(ID, RND, SK). If however the immobilizer control unit is programmed such that, after a first unsuccessful recognition attempt, it provides the same RDN and SIG numbers previously provided, it will never be possible to obtain the SK number starting from the inverse function f−1.
Another drawback consists of the fact that the immobilizer control unit memorizes an error representing an anomalous fact and could result in unforeseeable consequences by the control unit.
Another drawback consists of the fact that if the original key also presents mechanical notching, the new key must be notched mechanically before starting electronic duplication, independently of whether this can have a positive conclusion.